DSLR Lens Questions

[Mav359]

Hi guys

Since i moved to my QHY8L i haven't used my 1000d for much. Ive bought the bracket to mount the DSLR on the top of the OTA to take some wide field shots, whole constellations & landscapes that sort of thing. ive only got the basic 18-55mm lens that comes with it. I had a really basic go with it but struggled to get it to focus...... any suggestions?

Also i was thinking of getting one of these.....

http://www.ebay.co.uk/itm/Wide-Angle-Lens-4-Canon-1000D-1855mm-IS-G10-G12-W58-/121204776354

worth it?

[baggywrinkle]

I set up my camera on a tripod in daylight, a Canon 400D or my newer 650D and used the same lens. I chose some distant objects and tried the various focal lenghts, not all focus at the same infinity and if you go past infinity it is definately out of focus.

I made up a small table to ensure I could come back to the same point. On an older lens I made some tiny marks.

As you have a Canon and if you don't mind spending about £25 you can get Backyard EOS which is Canon dedicated and has a great focusing tool but you do need to be connected to a PC.

[jimmyjamjoejoe]

I wouldn't bother with the lens... They're typically poorly made, as are the cheap "close up" lenses.

Setting the kit lens to 24mm or so gives a pretty wide field while improving image quality compared to 18mm. Stop it down a touch, not too much or you'l struggle to get data, but wide open will leave soft edges.

As for focusing, does the 1000d have live view? If not, the best bet is to focus to infinity during the day, then set it to manual and dont touch it. :-)

[jgs001]

With the kit lens, or with the 50mm, use liveview, find a really bright star (it'll need to be)... zoom in to 10x on liveview, and with the lens set to MF (don't try this on AF as you can easily damage the AF drive gear) carefully and slowly tweak the focus ring until the bright star is the smallest blob you can make it. 

Rather than adding that converter to the mix, I'd take a look at the EF50 f/1.8 (aka nifty fifty, or plastic fantastic)... Seriously cheap for a seriously good piece of glass. You will need to stop it down to f/4 or f/4.5 to avoid the optical aberations around the edge of the field of view though. The FOV is about right for fitting in pretty much all of Orion for instance. 

Most, if not all modern lenses, allow for focus past infinity... I understand this is to allow for temperature fluctuations, so turning the focus ring to the end stop, is going to be out of focus.

[Steve Ward]

Plug the camera into the laptop and use EOSUtilities that came with the camera , aim at a bright star  Vega or similar and then tweak the focus using the controls in Utilities , take a 5 or 10 second test shot to check focus and adjust as required .

[Alien 13]

An alternative is to buy a used M42 lens and adapter the manual lenses have a fixed infinity hard stop which in some cases is adjustable i use them with good results.

[Mav359]

Cheers for all the advice guy's i'll get on and have a play

[Bhm2344]

I would say yes to the f1.8 50mm, I have one myself. I also have a sigma 70-300 and now an 18-135, as I've just got an EOS 60D. Out of the 3 I use the Sigma more. The 18-135 is EFs, and it won't let me use my astronomik cls filter

[jgs001]

Alan, one other thing, if you're kit lens has IS, make sure you turn it off. Some lenses are able to detect a steady mounting and disable the IS, but it has caused me issues, so I turn IS off when on a steady mounting... Given that you're mounting on a tracking mount, the IS will almost certainly get confused and activate.

[Gina]

I second the use of vintage M42 Pentax/Praktica thread mount film SLR lenses for AP.  The better makes such as Asahi Pentax SMC Takumar or Zeiss (I'm told) give good results.